Telson

Definition

The terminal, unsegmented division of the arthropod body, located posterior to the last true somite and bearing no appendages. Unlike true segments, the telson does not arise from teloblast areas during embryonic development. It typically forms part of the tail complex, often carrying a caudal furca or serving as an attachment site for tail fan musculature.

Etymology

Greek telson (τέλσον), 'boundary, limit'

Example

In scorpions, the telson is modified into a bulbous vesicle containing the venom gland and terminating in the aculeus (stinger); in decapod crustaceans, it forms the central plate of the tail fan between the uropods.

Synonyms

• anal somite (dated)
• terminal segment (loose)

Related Terms

• Pygidium
• uropod
• caudal furca
• opisthosoma
• Abdomen
• postabdomen
• tagma

Usage Notes

Usage varies by arthropod group. In crustaceans and xiphosurans, 'telson' is standard for the tail spine or plate. In insects and arachnids, the term is sometimes avoided in favor of 'terminal filament' or 'anal somite' when the structure is reduced or fused. The telson is never a true segment—this distinction matters in comparative embryology and phylogenetic discussions of arthropod segmentation. Contrast with pygidium, which is a true fused terminal segment in some taxa.